In a large pot of boiling water with Salt (to taste), add Spaghetti (250 gram). Cook for 10 minutes, or until the pasta is tender. Drain and return to pot.
In a mixing jug, add the Egg (3). Lightly beat until gooey. Add Parmesan Cheese (1 cup) and Cream (1 cup). Mix together.
Add zest and juice of Lemon (1). Whisk together.
In the pot with the spaghetti, add Butter (50 gram). Stir until melted, and then add the sauce. Mix until pasta is coated and sauce starts to thicken.
Top with Parmesan Cheese (to taste).